Due to rapid advance in the manufacture technology, several types of light-production equipments have been invented, among them is an LED. The LED has a relatively small size, a considerable long service life, and swift response. In addition, since the LED consumes lesser power, requires low voltage to drive the same and is tolerable to high vibration, the use of LED is prospective day by day.
Referring to FIG. 1, a fragmentary sectional view of a conventional LED assembly is shown to include a support member 11, an LED unit 10 disposed on the support member 11, and an encapsulating body 12 covering the LED unit 10.
The LED unit 10 generally includes a support plate 101, an N-type semiconductor layer 102 disposed on the support plate 101 and a P-type semiconductor layer 103 bonded to a selected region of the N-type semiconductor layer 102 such that the semiconductor layers 102, 103 have an N-type electrode 1021 and P-type electrode 1031.
The support member 11 has positive and negative ends 111, 112. The N-type and P-type electrodes 1021, 1031 of the semiconductor layers 102, 103 are respectively and electrically connected to the negative and positive ends 111, 112 of the support member 11. The encapsulating body 12 can be made from epoxy resin and hermetically encloses the LED 10 unit therein.
When the positive and negative ends 111, 112 of the support member 11 are connected to a power source, the free electrons and the holes respectively flow into the N-type and P-type layers 102, 103 and combine together, thereby causing electrons flow between the electrodes and consequently producing visible light beams.
By virtue of an external power source and a proper biasing, the conventional LED assembly is adapted to produce light beams continuously.
As explained above, the conventional LED assembly is said to be forward biasing, i.e. the LED assembly is illuminated only when the positive cycle of current flows into the positive end 111 of the support member 11.
The power source available and existing around us is Alternating Current, which provides negative and positive cycles alternately. In case the conventional LED assembly is used as an illuminating device (such as a light bulb), an AC/DC adaptor must be employed in order to provide stable lighting effect thereof. Utilization of the adaptor can therefore results in extra expense and restricts the usage range of the conventional LED assembly.